I don't think you can just pass '(i) to palindrome? here - doesn't the number need to be converted to a list of digits first? I got #t for everything using your code.

I took some code off SO and it bumped up the runtime substantially:

  #lang racket
  (require srfi/1 srfi/26)
  (define (digits->list num (base 10))
    (unfold-right zero? (cut remainder <> base) (cut quotient <> base) num))

  (define (palindrome? lst)
    (equal? lst (foldl cons empty lst)))

  (define ITERATIONS 10000000)
  (for ([i (in-range ITERATIONS)])
    (palindrome? (digits->list i)))

  racket palindrome.rkt  11.66s user 0.55s system 99% cpu 12.293 total

I'm a racket beginner so I'd be interested in better answers to this.